There are frequent medical situations in which it is desirable to insert a device into the vasculature, organ cavity, or other tubular body structure in a human or animal patient for diagnostic or for medical treatment procedures. Example procedures may include the placement of a catheterization or cannulation device into a part of the circulatory system (the vasculature), heart catheterization, urinary track catheterization, angioplasty, among numerous such other medical/diagnostic procedures. Some of these situations involve a short-term placement while others can extend over days or weeks. In the case of a cardiac patient, for example, modern practices often call for the use of a leg inserted arterial catheter and radio opaque dye for early diagnostic purposes or long-term catheter placement for antibiotic medication administration.
One of the difficulties frequently encountered in the placement of such catheters is said to involve the possibility of the catheter not being located in the intended position and in the intended configuration. For example, the moving catheter may follow an intended vein path for a few centimeters and then enter an unintentional branch vein path or double back on itself in a larger vein and thus have a terminal end located in an incorrect position. Because certain drug administration in some situations is location sensitive (because of tissue harm issues) either of these possibilities is undesirable.
In addition to these initial placement issues, the medical community for several reasons favors the placement of peripherally inserted central catheter (PICC) lines within the body as a means of administering treatment as opposed to use of the alternate central venous catheter (CVC) line because of the reduced risk of infection incurred and the fact that the PICC line can be placed by a nursing staff member instead of by a more expensive clinician such as an interventional radiologist. A PICC line can remain in place for many weeks with little concern for systemic infection or other medical complication. PICC treatment is favored because the patient can be placed in the home or low intensity medical facility with this type of line in place.
The PICC line procedure is generally preferred over the CVC procedure for administration of medical treatment. The PICC procedure is not without complication however. The most common difficulty with this procedure is in the uncertainty of the location and the orientation of the PICC line tip. It is not uncommon for a PICC tip to double back on the catheter so that it points in the wrong direction or is pointing into the wrong vein. As a response to this difficulty, a radiologist often confirms the placement of the line after initial insertion using two radiographs. One is take in an antero-posterior orientation and the second in a latero-medial orientation. With these two ninety degree separated views the radiologist can usually discern the location and placement of the distal end of a PICC line.
Unfortunately, however, normal bodily movements can alter the initial orientation and to some extent the placement a thin PICC line. Therefore, it is common for a radiologist to determine the correct placement and orientation of such a line before each treatment or measurement is made. This is time consuming and expensive and carries the added risk to the patient of undesired exposure to ionizing radiation. Therefore, the radiology procedure is often omitted because of reducing patient exposure to x-radiation, limited radiologist time, limited funding, and so-on. A method providing the same information and not requiring radiographic examination is needed.
In addition detection and tracking of catheter or cannulation devices, such as a CVC, in the human body has heretofore been performed by various techniques including the use of x-ray, RF, magnetic resonance, induction and magnetic field, and infrared light. The most common practice is x-ray imaging of a radiopaque cannula that appears in high contrast compared to surrounding structures on a radiographic image. In this procedure the detail and course of the cannula is compared to known structural landmarks of the body, including bone, dense tissue and body margins in order to direct the cannula by x-ray to the intended endpoint. This method can confirm accurate placement of a distal cannula tip terminating in the superior vena cava, but utility of this method is limited if the x-ray exposure time becomes so lengthy as to expose patient and attending practitioner to significant radiation levels.
The distal end of a catheter may also be detected magnetically with a Hall Effect probe or similar magnetic sensor, and may also be detected, though with difficulty, in a space containing air, using ultrasound (U.S. Pat. No. 4,344,436 to Kubota) or radio frequency signals (U.S. Pat. No. 5,377,678 to Dumoulin et al). The general location of the distal end of the catheter can be detected using these methods, but the sensor must be scanned over the patient either during insertion or placement to locate the approximate location of the distal end.
Radio frequency (RF) detection of catheter location, as in U.S. Pat. Nos. 5,377,678 and 5,211,165 to Dumoulin et al, utilizes a transmit coil at the distal end of the catheter, the coil being driven by a low RF energy source that generates an electromagnetic field detectable by either a single or an array of receiver antennae distributed near the body area of interest. A receiver connected to the antennae provides signals that define catheter position and orientation. The positional data are merged with imaging data from radiography to enhance catheter location and orientation in order to minimize overall radiographic exposure. The RF method may, however, result in elevated temperatures in the core of the body during the course of a catheter insertion by way of a diathermy-like process. Utility of the method may be further limited by impedance mismatch between the RF driver and the coil or antenna that limit the strength of signals from the antenna. The procedure also involves both RF and x-ray imaging and thus compounds the instrumentation and operator skills needed to compile location and tracking data and requires x-ray exposure to the patient.
Detection and tracking of catheter location by magnetic resonance (as in U.S. Pat. Nos. 5,307,808 and 5,318,025 to Dumoulin et al, and 5,715,822 to Watkins et al) generally comprises detection of local magnetic resonance response signals via a small RF coil positioned within the body in a larger magnetic resonance field. The patient is subjected to a large-scale magnetic field that induces local responses detected by the small-scale RF coil contained near the catheter distal end. Location is derived from analysis of varying magnetic resonance pulse gradients and requires precision electronics and signal analysis systems, as well as costly computational and imaging tools, including large-scale magnetic resonance imagers with superconducting magnets, and is limited by the short range of the RF coil that allows only limited field-of-view images.
Detection and tracking of a catheter using magnetic coils or objects (as in U.S. Pat. Nos. 4,173,228 to Van Steenwyk et al, 5,125,888 to Howard et al, 5,425,367 to Shapiro et al, 5,645,065 to Shapiro et al, and 6,226,547 to Lockhart et al) generally comprise either measurement of an induced magnetic field in a coil fixed to a catheter within the body or disposed outside the body. At least two interacting component groups are required including at least one energized magnetic output coil and at least one sensor coil to detect the field of the output coils. The output coils may be located near the end of the catheter within the body and the sensor coils near the output components exterior of the body, or the sensors may be affixed to the catheter and the output coils exterior of the body. The exterior sensors must be either scanned over the body or distributed at multiple sites in order to properly measure the strength and orientation of the output signal.
Applying RF energy to coils located within the body potentially exposes the body to large voltages and the associated electric fields that may interfere with body functions or with other monitoring devices. Energizing the sensors outside the body can require a complex arrangement of magnetic transducers that may occupy critical space in the course of medical procedures. In general, such magnetic field detection arrangements rely primarily on proximity between output and sensor components and therefore do not provide complete assessment of the body, but only of portions where exterior components are applied. Furthermore, proximity between components may be difficult to achieve, as a result of physical interference from local or extended medical devices, from materials such as dressings, castings, and electrocardiogram electrodes, from anatomical features such as obesity and dense bone structures and as a result of magnetic fields associated with electrical instrumentation or other or electrical devices.
Detection and tracking of a catheter using near-infrared (NIR) light, is described in U.S. Pat. Nos. 5,517,997 to Fontenot and 6,597,941 to Fontenot et al., and is accomplished using a light guiding catheter inserted into the lumen of, for example, the ureter and involves emitting NIR light from the endpoint of the catheter. Light transilluminating such a ureter is detected by a sensor and highlights the transgressed lumen and surrounding tissue of the body structure. Generally, this method is useful for protection of the transgressed structure or the various body parts lying adjacent to the transgressed regions, and is limited in these particular applications to body intrusive procedures for protection purposes.